Visible Light Absorption Range Research Articles

Spiky TiO2/Au nanorod plasmonic photocatalysts with enhanced visible-light photocatalytic activity.

A facile approach for the preparation of spiky TiO2/Au nanorod (NR) plasmonic photocatalysts has been demonstrated, which is through in situ nucleation and growth of spiky TiO2 onto AuNRs. Different aspect ratios of AuNRs in 2.5, 2.7, 4.1 and 4.5 have been applied to prepare spiky TiO2/AuNR nanohybrids to achieve tunable and broad localized surface plasmon resonance (LSPR) bands. All spiky TiO2/AuNR nanohybrids exhibit enhanced light harvesting by extending visible light absorption range by both transverse and longitudinal LSPR bands and decreasing light reflectance by their unique spiky structures. Compared to the bare AuNRs, commercial TiO2 (P25) and spiky TiO2/Au nanosphere photocatalysts, the spiky TiO2/AuNR photocatalysts exhibit significantly enhanced visible light photocatalytic activity in Rhodamine B (RhB) degradation due to their simultaneous enhancement in the light harvesting, charge utilization efficiency, and substrate accessibility. In particular, the spiky TiO2/AuNR-685 photocatalysts show the best photocatalytic activity with ∼98.9% of the RhB degraded within 90 min under the irradiation of 420-780 nm, which could be ascribed to the most extended visible light absorption range and sufficient photon energy of TiO2/AuNR-685 photocatalysts within this irradiation region. The bio-inspired nanostructure, as well as the facile and scalable fabrication approach, will open a new avenue for the rational design and preparation of high-performance photocatalysts for pollutant removal and water splitting.

Exploration of silver decoration concentration to enhance photocatalytic efficiency of titanium dioxide photocatalysts

Ag decoration on TiO2 is favorable to absorption of visible light and wider absorption range. Ag nanoparticles playing the role of electron receivers on TiO2 surface enhance photodegradation. However, excess Ag nanoparticles caused reduced specific surface area of photocatalysts and increased probability of charge recombination, resulting in lower photocatalytic efficiency. In this study, the influence of various Ag decoration concentrations on photocatalytic activity was investigated. Surface treatment by nitric acid after Ag decoration was performed to avoid excessive Ag deposition. The extent of Ag elimination and its impacts on photocatalytic activity were also explored. An optimum Ag content in the photocatalyst was achieved and photocatalytic efficiency was obviously improved. It was found that the number of calcination times affected the crystallinity and stability of photocatalysts. Better photocatalytic efficiency could be obtained after twice calcinations.

Enhancement in Rate of Photocatalysis Upon Catalyst Recycling.

Recyclability is an important aspect for heterogeneous photo-catalysts. Ease of recovery and stability of the photo-catalyst in terms of efficiency over the number of cycles are highly desired and in fact it is ideal if the efficiency is constant and it should not decrease marginally with each cycle. Presented here is a seminal observation in which the photocatalytic activity is shown to improve with increasing number of catalytic cycles (it is 1.7 times better after the 1st cycle and 3.1 times better after the 2nd cycle). Specifically, nanorods of pure TiO2 and TiO2 doped with controlled amount of tungsten have been used to degrade two model pollutants: Phenol and Rhodamine B under exclusive visible light illumination. It was found that, in case of 1 mol.% W incorporation, rate of photocatalysis and also the range of visible light absorption of the photocatalyst increased after the photocatalysis as compared to before photocatalysis. This aspect is unique for doped TiO2 and hence provides an intriguing way to mitigate low photoactivity.

Triton X-100 induced cuboid-like BiVO4 microsphere with high photocatalytic performance

A highly active visible light-induced BiVO4 photocatalyst was prepared by a simple co-precipitation method using ammonia solution as a pH adjustor and Triton X-100 (TX100) as a structure directing agent. The physical properties of the prepared BiVO4 photocatalyst were investigated by several techniques such as X-ray diffractometer (XRD), Brunauer–Emmett–Teller (BET) surface area measurement, scanning electron microscopy (SEM), energy dispersive analysis (EDS), Fourier-transformed infrared spectroscopy (FT-IR), photoluminescence (PL), and UV–Vis diffused reflectance spectroscopy (DRS). XRD results revealed the existence of a monoclinic scheelite structure in both the unmodified and the modified samples. The TX100 played a crucial role to control the cuboid-like shape morphology of BiVO4. The DRS results showed that the as-prepared cuboid BiVO4 possessed enhanced visible light absorption range compared with that of the unmodified BiVO4. The photocatalytic activity was evaluated via indigo carmine (IC) degradation under visible light irradiation. The modified BiVO4 showed higher photocatalytic efficiency than the unmodified BiVO4 and the commercial P25-TiO2 which could be ascribed to the better charge separation efficiency.

Synthesis of nanoporous carbon nitride using calcium carbonate as templates with enhanced visible-light photocatalytic activity

A commercial calcium carbonate particle as hard template is employed to synthesize mesoporous carbon nitride (mpg-C3N4) by a thermal polycondensation process using dicyandiamide as a precursor, then it can be easily removed using diluted hydrochloric acid. Compare with the other hard templates, such as SiO2 and porous anodic aluminium oxides (Al2O3), the industrially available calcium carbonate particles are not only low-cost, but also environment friendly. A certain amount of carbon dopants were generated in the resulting mpg-C3N4 matrix, and the concentration of carbon dopants can be controlled by the amount of calcium carbonate particle. The synthesized mpg-C3N4 not only possesses high specific surface area, but also has the enhanced visible light absorption range from 460nm to 800nm. The photocatalytic activity increases as the mass ratio of template to dicyandiamide increases, when the mass ratio is 1.0, the photocatalytic performance is up to the maximum, which is 12.3 times higher than that of bulk g-C3N4. The enhancement of the photocatalytic performance of mpg-C3N4 is contributed to its improved specific surface areas and the enhancement of the visible light absorptions from 450nm to 800nm.

Sonication-polished anodic TiO2 nanotube array-based photoanode for efficient solar energy conversion

In this work, the capping layer atop anodic TiO2 nanotube arrays (NTAs), which hinders filling of other guest materials and transport of charge carriers, is discerned to be TiO2 nanotapes. Then, it is completely removed by a novel sonication-polishing (SP) treatment, after which Sb2S3 is subsequently introduced to fill the nanotubes by chemical bath deposition. The morphological, structural, and optical properties of the SP-treated TiO2 NTAs and TiO2 NTAs/Sb2S3 heterogeneous structures are characterized systematically. The results indicate that SP treatment opens the tops of nanotubes with diameters of ∼120 nm, which endure a phase conversion from amorphous to anatase after calcination at 450 °C; besides, stibnite Sb2S3 with a band gap of ∼1.75 eV inside the TiO2 networks is formed upon heat treatment at 330 °C in Ar, which enhances the absorption in visible light range. The photoelectrochemical (PEC) and photovoltaic properties for the SP-treated TiO2 NTAs are investigated. Results shows that the photoresponse of TiO2 NTAs is improved by the SP treatment, and the photocurrent for the TiO2 NTAs/Sb2S3 electrode is substantially enhanced as compared to the bare TiO2 one. A high efficiency of 6.28 % is achieved in a TiO2 NTAs/Sb2S3 PEC cell. In addition, charge recombination in the photoanode of dye-sensitized solar cells (DSSCs) is observed to be greatly retarded by using the SP-treated TiO2 NTAs as compared to TiO2 nanoparticles (NPs). Thus, the SP anodic TiO2 NTAs are promising in applications in various PEC areas such as photocatalysis and sensitized solar cells.

Synthesis of CuO micro-sphere combined with g-C3N4 using Cu2O as precursor for enhanced photocatalytic hydrogen evolution

The CuO micro-sphere combined with the g-C3N4 to form the p-n heterojunction was first prepared by the simple impregnation–calcination technique. The SEM and XPS revealed the tight combination between CuO micro-sphere and g-C3N4. The UV spectra and PL spectra confirmed the obvious red shift to improve visible light absorption and effective light-induced carriers separation. The hydrogen evolution rate was improved more than 100% compared with pure g-C3N4. It is revealed that the more broad visible light absorption range and the p-n heterojuction mechanism was the key factor to facilitate the photocatalytic performance of hydrogen evolution.

Two-dimensional assembly structure of graphene and TiO2 nanosheets from titanic acid with enhanced visible-light photocatalytic performance

The titanic acid sheets were prepared by one-step hydrazine hydrate-assisted hydrothermal process. Then the reduced graphite oxide (rGO)@TiO2 nanosheet composites were finally obtained through ultrasonic exfoliation and following calcination treatment process. rGO@TiO2 nanosheet composites show excellent hydrogen production performance under AM1.5 light source. The highest hydrogen evolution yield (923.23μmol) is nearly two times higher than that of pure TiO2, mainly due to the special electron structure and more active sites for TiO2 nanosheet. The introduction of graphene could improve the TiO2 nanosheet stability and extend visible-light absorption range.

Iodinated SnO2 Quantum Dots: A Facile and Efficient Approach To Increase Solar Absorption for Visible-Light Photocatalysis

Efficient visible-light-driven photocatalysis can be achieved over conventional wide band gap semiconductor, in which iodinated SnO2 quantum dots (QDs) are synthesized via hydrolysis of crystalline SnI4 in the absence of any additives or templates. The formation of SnO2 QDs reveals a wide preparation window and a very fast growth rate in minute scale. The iodine species may only exist on the surface of SnO2 QDs, which can be completely removed through heat treatment. SnO2 QDs reveal the light absorption in visible range which increases the limited optical absorption of bulk SnO2. Notably, the iodination can further enhance the visible light absorption due to the formation of band tail states. Therefore, iodinated SnO2 QDs exhibit significantly enhanced visible-light-driven photocatalytic activity toward degradation of rhodamine B and oxidation of NO in ppb level. Time-resolved spectroscopic studies reveal that the iodine species in QDs can not only server to passivate the surface traps to prolong the life...

ZnO nanorod arrays co-loaded with Au nanoparticles and reduced graphene oxide: Synthesis, characterization and photocatalytic application

Abstract ZnO nanorod arrays (NRAs) co-loaded with Au nanoparticles (NPs) and reduced graphene oxide (RGO) are fabricated using a simple one-step electrochemical deposition method. The obtained photocatalysts were characterized by field emission scanning electron microscopy, X-ray diffractometer, photoluminescence and UV–vis absorption spectra. The photocatalytic activity of the as-prepared samples was investigated by degradation of methylene blue under visible light irradiation. The results showed that Au/RGO–ZnO NRAs exhibited much higher photocatalytic activity than RGO–ZnO NRAs, Au–ZnO NRAs and pure ZnO NRAs. The synergistic effect of Au NPs and RGO enhances visible light absorption range and transmits the hot electrons more efficiently. This research will encourage more rational design of efficient visible light responsive photocatalysts.

Synthesis of stoichiometric AgSbS2 nanospheres via one-step solvothermal chemical process

Abctract High quality ternary chalcogenide AgSbS 2 nanospheres have been synthesized via a one-step, facile and practical solvothermal chemical process by using 3-aminopropyl triethoxysilane(APTS) self-assembly monolayers(SAMs) as templates. The surface morphology, structure and composition of the resultant AgSbS 2 nanospheres were characterized by FESEM, XRD and XPS, respectively. The results show that the nearly stoichiometric AgSbS 2 nanospheres possess pure cubic structure with high crystallinity. The –NH 2 terminal groups of APTS could provide nucleation sites for the growth of AgSbS 2 nanospheres and the slow release of Sb 3+ in the solution could promote the isotropic growth of AgSbS 2 crystal. AgSbS 2 nanospheres exhibit a broad absorption in visible light range, making it a promising photovoltaic absorber material.

Characterization and photoactivity of Pt/N-doped TiO2 synthesized through a sol–gel process at room temperature

The rates of photocatalytic production of H2 by Pt/N-doped TiO2 are significantly affected by the hydrolysis temperature applied during the sol–gel process. Production rates increase as the hydrolysis temperature decreases from 40 to 20 °C. The effects of the hydrolysis temperature on the properties and water-splitting behavior of photocatalysts were investigated. Characterization results showed that hydrolysis temperatures higher than 40 °C induce the formation of the rutile phase and particle agglomeration, reduce the N-dopant content, and decrease the range of visible-light absorption. In this study, a low hydrolysis temperature of about 20 °C is optimal for the sol–gel preparation of N-doped TiO2; this temperature favors the formation of high-purity anatase, small particle size, extensive visible-light absorption, and excellent rates of photocatalytic production of H2 (about 2100 μmol h−1 g−1).

Highly efficient and stable cyclometalated ruthenium(II) complexes as sensitizers for dye-sensitized solar cells

Four novel thiocyanate-free cyclometallted Ru(II) complexes, D-bisCF3, D-CF3, D-OMe, and D-DPA, with two 4,4′-dicarboxylic acid-2,2′-bipyridine together with a functionalized phenylpyridine ancillary ligand, have been designed and synthesized. The effect of different substituents (R=bisCF3, CF3, OMe, and DPA) on the ancillary C^N ligand on the photophysical properties and photovoltaic performance is investigated. Under standard global AM 1.5 solar conditions, the device based on D-CF3 sensitizer gives a higher conversion efficiency of 8.74% than those based on D-bisCF3, D-OMe, and D-DPA, which can be ascribed to its broad range of visible light absorption, appropriate localization of the frontier orbitals, weak hydrogen bonds between -CF3 and -OH groups at the TiO2 surface, moderate dye loading on TiO2, and high charge collection efficiency. Moreover, the D-bisCF3 and D-CF3 based DSSCs exhibit good stability under 100mWcm−2 light soaking at 60°C for 400h.

Improved visible-light photocatalytic activity and anti-photocorrosion of CdS nanoparticles surface-modified by conjugated derivatives from polyvinyl chloride

Cadmium sulfide (CdS) nanoparticles were surface-modified by conjugated polymer (CPVC) derived from conventional polyvinyl chloride (PVC) via heat-treatment at 150°C. The as-prepared CPVC/CdS nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (UV–vis DRS), photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS), and photocurrent (Iph). The visible-light photocatalytic activity and stability of the nanocomposites were investigated by evaluating photodegradation of methyl orange (MO) and phenol, and their anti-photocorrosion performance was investigated by determining the concentrations of Cd2+ in the photodegrading systems under visible light irradiation. The results show that a small amount of CPVC on the surface of CdS nanoparticles hardly changes their crystallinity and sizes, while significantly improves their absorption in visible light range and separation efficiency of photogenerated electrons and holes. The CPVC/CdS nanocomposites exhibit much higher visible-light photocatalytic activity and anti-photocorrosion performance than pure CdS, and show good visible-light photocatalytic stability. The visible-light photocatalytic mechanism has been discussed.

Investigation of nitrogen doped and carbon species decorated TiO2 with enhanced visible light photocatalytic activity by using chitosan

Nitrogen-doped and carbon species decorated TiO2 composites (Cts/TiO2) are prepared by using chitosan as a natural nitrogen and carbon source to combine with TiO2 by a facile and low-cost method for the first time. Their structures and properties are characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption isotherms (BET), and electron spin resonance spectroscopy (ESR). The results show that the visible light absorption range of the composites even can be extended to 650nm. Photocatalytic degradation of Rhodamine B (RhB) under visible light (420nm<λ< 800nm) irradiation is used as a model reaction to evaluate the photocatalytic activity of the composites. When the additive amount of chitosan is 0.25g, the sample Cts/TiO2-25 possesses the highest activity, which is over 4.8 times of N-TiO2. The detection of active species during the photocatalytic process shows that superoxide radicals (O2−) play the most important role, then the probable degradation mechanism of the photocatalysts is proposed simultaneously. It is hoped that our work will open a new doorway to use a simple and green method to get high-efficiency TiO2-based photocatalysts.

A facile synthesis of AgxAu1−x/TiO2 photocatalysts with tunable surface plasmon resonance (SPR) frequency used for RhB photodegradation

A series of AgxAu1−x/TiO2 photocatalysts with tunable surface plasmon resonance (SPR) frequencies were successfully prepared via a facile photoreduction combined with a simple replacement reaction between Ag and Au3+ ions. These two reactions react synergistically, resulting in the formation of Ag–Au alloy on TiO2. The as-prepared AgxAu1−x/TiO2 plasmonic photocatalysts exhibiting different colors absorb the visible light with different wavelengths, improving the utilization efficiency of the incident light with distinct frequencies. For RhB degradation, these catalysts containing Ag–Au alloy show much higher visible light-responsive photocatalytic activity than the commercial P25 and the single supported Ag or Au catalysts. By mixing the catalysts AgxAu1−x/TiO2 with different SPR frequencies, the photocatalytic activity can be further improved due to the widened visible light absorption range.

Enhanced photoelectrochemical and sensing performance of novel TiO2 arrays to H2O2 detection

Ag-decorated TiO2 nanowire arrays were facilely prepared by H2O2 corrosion of Ti and subsequent photodeposition of Ag. Array structures and photoelectric properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis absorption spectroscopy and electrochemical methods. These results show that Ag quantum dots are evenly distributed on the surface of TiO2 nanowires. With an Ag content of 0.4at%, the electrode's photocurrent density and photoconversion efficiency obtained optimum values of 0.29mA/cm2 and 8.55%, respectively. The enhanced photoelectrochemical properties with Ag modification can be attributed to the extended visible light absorption range and improved separation of photo-generated carriers. Additionally, the modified nanowire arrays exhibited much stronger photoelectrocatalytic reduction activity toward hydrogen peroxide in comparison with pure TiO2 arrays or previously reported Ag electrodes.

Hydrogenation of Nano-Structured TiO2 Photocatalyst Through an Electrochemical Method.

Nano-structured photocatalyst P25 was electrochemically hydrogenated through being immersed in 0.01 M NaOH solution to act as cathode to electrolyze water. With its color changed from white to bluish, its absorption in visible light range was obviously enhanced after the treatment, and its solar-driven photocatalytic activity was significantly improved for photo-degradation of methylene blue and rhodamine B. XPS spectra analyses were conducted and the photocurrent was measured, which indicate the formation of Ti3+ and oxygen vacancies, and increased separation efficiency of photoactivated electrons and holes in electrochemically hydrogenated P25. These changes are proposed responsible for the improved photocatalytic activity of P25. Electrochemical hydrogenation has been proven a facile and effective method for improving the photocatalytic activity of nano-structured TiO2 photocatalyst.

Thin carbon layer coated Ti(3+)-TiO2 nanocrystallites for visible-light driven photocatalysis.

Black TiO2 containing Ti(3+) attracts enormous attention due to its excellent visible-light driven photocatalytic activity. Herein, an in situ thermal decomposition approach to synthesize uniform thin carbon coated Ti(3+)-TiO2 nanocrystals is presented. During the oleic acid-assisted solvothermal process, the crystal size and morphology of TiO2 were controlled through oleic acid with carboxylic acid groups. Then the residual small quantities of oleic acid anchored on TiO2 were used as a carbon source, which could be in situ pyrolyzed into a carbon layer on TiO2 at high temperature and under an inert atmosphere. Meanwhile, Ti(4+) species were partly reduced into Ti(3+) states/oxygen vacancies on the surface of TiO2 due to the carbothermal reduction reaction for the carbon-encapsulated Ti(3+)-TiO2 structure. A series of characterizations indicated that the 20-25 nm TiO2 nanocrystals obtained were wrapped evenly by 1-2 nm carbon layers, which had an important effect on the energy band structure change of TiO2. The presence of the carbon layer also improves the Ti(3+) stability and the conduction behavior of the composites. The Ti(3+) states/oxygen vacancies created on the surface of TiO2 were responsible for the remarkable photogenerated charge separation and extended visible-light absorption range. Furthermore, Ti(3+) states/oxygen vacancies and the carbon layer together could enhance the adsorption ability of O2 so as to promote the photogenerated electrons captured by the adsorbed O2, leading to a great increase in the charge separation. As a result, the composites exhibit high photocatalytic performance for organic pollutants under visible light irradiation. This simple and new method may pave the way to practical applications for efficient photocatalytic degradation under visible light.

Colored titania nanocrystals and excellent photocatalysis for water cleaning

Colored titania has attracted enormous attentions due to its visible light absorption and wide range of applications. Here, we demonstrate an effective approach to obtain colored titania with enhancing solar absorption by introducing disorder in the surface of titania through Al reduction. As prepared black TiO2−x possesses solar energy absorption up to 88%. The recombination centers of light-induced electrons and holes are reduced in acid solution, which ensures the excellent photocatalytic activity of the black TiO2−x in the photo-oxidation of organic molecules in water.